This invention relates to a naphthalocyanine derivative, a process for producing the same, an optical recording medium using the same, and a process for producing the optical recording medium.
In recent years, it has been proposed to utilize diode laser beams for writing and reading in compact discs, video discs, liquid crystal display devices, optical reading machines etc. and as light source for electrophotograph. For writing or reading by use of diode laser beams, a substance capable of absorbing diode laser beams, i.e., near infrared rays is indispensable.
As organic dyes which absorb near infrared rays, cyanine dyes have heretofore been well known, and metal complexes of oximes and thiols and aminated quinone derivatives are also known as dyes which absorb near infrared rays [Yuki Gosei Kagaku Kyokai Shi, vol. 43, p. 334 (1985), Shikizai Kyokai Shi, vol. 53, p. 197 (1980), and Shikizai Kyokai Shi, vol. 58, p. 220 (1985)].
However, the cyanine dyes have a very low stability against light and hence their employment has many restrictions. The metal complexes of oximes and thiols are disadvantageous in that the metals are released from the complexes in a certain medium, resulting in loss of the ability to absorb near infrared rays. The aminated quinone derivatives are very poor in ability to absorb near infrared rays.
On the other hand, as materials capable of overcoming these problems, naphthalocyanine derivatives have recently been known, but conventional unsubstituted metal naphthalocyanines [Zhurnal Obshchei Khimii, vol. 39, p. 2554 (1969) and Mol. Cryst. Liq. Cryst. 112, 345 (1984)]are insoluble in organic solvents and hence are very difficult to purify. Recently, synthesis of naphthalocyanine derivatives soluble in organic solvents has been reported (Japanese Patent Appln Kokai (Laid-Open) Nos. 60-23451, 60-184565, 61-215662 and 61-215663), but these naphthalocyanine derivatives have the following disadvantages. Their absorption varies greatly depending on the kind of solvent, concentration, temperature, etc., and in a solution having a high concentration or in the form of a solid film, their ability to absorb diode laser beams is greatly lowered and moreover the reflectivity which is important when reflected light is used for reading out information recorded in an optical disc is very low in the diode laser region (780 to 830 nm).
Only two compounds have been reported in Japanese Patent Appln Kokai No. 61-235188 as naphthalocyanines having a high reflectivity, and the concept of synthesis of these compounds has been reported in Japanese Patent Appln. Kokai Nos. 61-177287 and 61-177288, but only a small number of Examples are described therein and in few Examples, the compounds can be synthesized in the manner described therein. For example, in the case of the reaction formula I described in the first line in the right, top column on page 8 of Japanese Patent Appln Kokai (Laid-Open) No. 61-177288, when a long-chain alkyl group or the like is contained in Xn, the solubility of a starting material: ##STR2## is too large, and in synthesizing this material, isolation of the material from a reaction solution becomes impossible and moreover a reaction mixture in a synthesis step of a starting material: ##STR3## for the above-mentioned starting material is complicated, so that separation and purification of this compound from a reaction system becomes difficult. Therefore, it becomes impossible to use the starting materials for synthesizing a desired naphthalocyanine. The reaction formula II described in the third line in the right, top column on page 8 of Japanese Patent Appln Kokai (Laid-Open) No. 61-177288 shows a nucleophilic reaction of a naphthalocyanine ring which is similar to Friedel-Craft reaction, and it is not suitable for introduction of alkoxyl groups, alkylthio groups, and amino groups into a naphthalocyanine ring. Further, in the case of the reaction formula III described in the fifth line in the right, top column on page 8 of Japanese Patent Appln. Kokai (Laid-Open) No. 61-177288, purification of a starting material is impossible, and a product is obtained in the form of a very complicated mixture and is difficult to purify. Therefore, this reaction formula is not suitable for isolating a product of high purity, and moreover the reaction cannot be allowed to proceed in a desirable direction because the reaction itself is inhibited by the influence of a hydroxyl group bonded to Si of the starting material. Thus, there has been a problem that a synthetic method should be independently found for synthesizing naphthalocyanines particularly having a long-chain alkyl group in the naphthalocyanine ring which is actually soluble in organic solvents and has excellent characteristics as an optical recording medium.